Could be that the bearings on the fan are shot. My front case fan sounds like it is grinding on something when it is in use because the bearings are shot. My temporary fix was to slide a q-tip through the fan casing to stop the blades from spinning. My temperatures are still at a normal level, but I do plan on purchasing a new fan when I can part with the funds.

I wouldn't recommend doing this with the PSU fan, however.